Half fill a large pan with water. Add a pinch of salt. Cover and put on a high heat to come to the boil. Scrub and peel the potatoes (see our tip on what to do with your potato peelings). Chop the potatoes into equal-sized chunks, around 3-4cm across. When the water is boiling, add the potatoes. Bring to a gentle simmer, and then simmer for 5-6 mins.
Meanwhile, heat your oven to 200°C/Fan 180°C/Gas 6. Add 1 tbsp olive oil to a large roasting tin or 2 medium tins. Put them in the oven to heat the oil and butter for 10 mins.
Drain the potatoes, then tip them back into the pan. Put the lid on the pan and shake it gently a few time to rough the edges of the potatoes (be careful not to break the potatoes up too much).
Take the roasting tin out of the oven. Add the butter and swirl to melt it. Add the spuds. Season with a pinch of salt. Turn them a few times to coat in the hot oil and butter. Roast for 45 mins till they're golden brown. If you're using two tins, swap them over half way through cooking.
When the spuds are ready, transfer them to a serving bowl and serve straight away.